﻿<p>A site is a defined area of land, possibly covered with water, on which the project construction is to be completed. A site may be used to erect, retrofit
or turn down building(s), or for other construction related developments.</p>

<blockquote class="note">NOTE&nbsp; Term according to ISO6707-1 vocabulary "area of land or water where construction work or other development is undertaken".</blockquote>
 
<p>A site may include a definition of the single geographic reference point for this site (global position using WGS84 with <em>Longitude</em>, <em>Latitude</em> and <em>Elevation</em>). The precision is provided up to millionth of a second and it provides an absolute placement in relation to the real world as used in exchange with geospational information systems. If asserted, the <em>Longitude</em>, <em>Latitude</em> and <em>Elevation</em> establish the point in WGS84 where the point 0.,0.,0. of the <em>LocalPlacement</em> of <em>IfcSite</em> is situated.</p>

<p>The geometrical placement of the site, defined by the <em>IfcLocalPlacement</em>, shall be always relative to the spatial structure element, in which this site is included, or absolute, i.e. to the world coordinate system, as established by the geometric representation context of the project. The world coordinate system, established at the <em>IfcProject.RepresentationContexts</em>, may include a definition of the true north within the XY plane of the world coordinate system, if provided, it can be obtained at <em>IfcGeometricRepresentationContext.TrueNorth</em>.</p>

<p>A project may span over several connected or disconnected sites. Therefore site complex provides for a collection of sites included in a project. A site
can also be decomposed in parts, where each part defines a site section. This is defined by the composition type attribute of the supertype <em>IfcSpatialStructureElements</em> which is interpreted as follow:</p>
<ul>
<li>COMPLEX = site complex</li>
<li>ELEMENT = site</li>
<li>PARTIAL = site section</li>
</ul>
<p>The <em>IfcSite</em> is used to build the spatial structure of a
building (that serves as the primary project breakdown and is 
required to be hierarchical). </p>


<p>Figure 3 shows the <em>IfcSite</em> as part of the spatial structure. In addition to the logical spatial structure, also the placement hierarchy is shown. In this example the spatial structure hierarchy and the placement hierarchy are identical.</p>

<blockquote class="note">NOTE&nbsp; Detailed requirements on mandatory element containment and placement structure relationships are given in view definitions and implementer agreements.</blockquote>


<table summary="Spatial and placement structure">
 
<tr>
  <td valign="top"><img src="../../../figures/ifcsite-spatialstructure.png" 
   alt="IfcSite as part of a spatial structure" width="800" height="420" border="0">
  </td>
  </tr>
 
<tr>
  <td><p class="figure">Figure 3 &mdash; Site composition</p>
  </td>
 </tr>

</table>



<p>Figure 4 describes the heights and elevations of the <em>IfcSite</em>. It is used to provide the geographic longitude, latitude, and height above sea
level for the origin of the site. The origin of the site is the local placement.</p>
<p>The provision of longitude, latitude, height at the <em>IfcSite</em> for georeferencing is provided for upward compatibility reasons. It requires a
single instance of <em>IfcSite</em> and WGS84 as coordinate reference system.</p>
<p>For exact georeferencing (or referencing to any other geographic coordinate system other than WSG84) the entities <em>IfcCoordinateReferenceSystem</em> and
<em>IfcMapConversion</em> have to be used to define an exact mapping of the project engineering coordinate system to the geographic (or map) coordinate
system.</p>
<ul>
<li><small>reference height of site is provided by: <em>IfcSite.RefElevation</em>, it is given according to the height datum used at this location.</small></li>
<li><small>the reference height of each building situated at the site is given againt the same height datum used at this location.</small></li>
<li><small>the elevations of each storey belonging to each building are given as local height relative to the reference height of the building.</small></li>
</ul>
<table border="0" cellpadding="2" cellspacing="2" summary="attribute use">
<tbody>
<tr valign="top">
<td align="left" valign="top"><img src="../../../figures/ifcsite_heights.png" alt=
"building heights" border="0" height="400" width="500">&nbsp;</td>
</tr>
<tr>
<td>
<p class="figure">Figure 4 &mdash; Site elevations</p>
</td>
</tr>
</tbody>
</table>

<blockquote class="history">HISTORY &nbsp;New entity in IFC1.0.</blockquote>